(1) Field of the Invention
The present invention relates to inks which include an ingredient which changes color in response to different ambient moisture levels, and more particularly to a solution-type moisture indicating ink wherein the ink ingredients are in solution and which can be printed at a high rate upon the substrate.
(2) Discussion of the Prior Art
Various inks or coating which change color are known per se. Examples of such heretofore known and their uses are disclosed in the following United States Patents.
U.S. Pat. No. 650,901, issued on June 5, 1900 to Ernest Kretschmann.
U.S. Pat. No. 2,228,033, issued on Jan. 7, 1941 to Thomas A. Martone.
U.S. Pat. No. 3,216,802, issued on Nov. 9, 1965 to Charles J. Smith.
U.S. Pat. No. 3,360,339, issued on Dec. 26, 1967 to Martin Edenbauum.
U.S. Pat. No. 3,499,316, issued on Mar. 10, 1970 to W. O. Krause.
U.S. Pat. No. 3,548,639, issued on Dec. 22, 1970 to W. O. Krause.
U.S. Pat. No. 3,881,873, issued on May 6, 1975 to Iris B. Klowden.
U.S. Pat. No. 4,643,122, issued on Feb. 17, 1987 to Paul G. Seybold.
U.S. Pat. No. 650,901 teaches an ink consisting of a solution of the halide salts of cobalt, glycerin, gum arabic and water. A paper is coated with this solution. This ink is developed using a developing ink of resorcinol and paratoluidine, water, and sulfuric acid.
U.S. Pat. No. 2,228,033 teaches an ink which is normally invisible when printed on fabrics and paper, but becomes visible when wetted with a solution. This patent more particularly teaches cellulose nitrate or acetate or various gums and solvents such as amyl alcohol, butyl alcohol, their esters, and, glycol ethers. The ink also includes a colorless gum or resin or cellulose derivative in a volatile water soluble monohydric alcohol, preferably, ethyl cellulose in methyl or ethyl alcohol. When the ink is printed on paper, it is invisible, and becomes visible when wetted by water. The ink consists of a volatile alcohol of the group consisting of methyl and ethyl alcohol, and alcohol soluble cellulose ether.
U.S. Pat. No. 3,216,802 teaches a reagent for determining the moisture content of paper. The reagent is a solution of cobaltous chloride in a non-aqueous volatile solvent which is placed in contact with a fibrous web (such as paper) and the solvent allowed to evaporate so that the residue of cobaltous chloride remaining on the fibrous web will undergo a color change which is directly related to the moisture content of the fibrous web. The solvent may be methanol, ethanol, acetone or mixtures thereof.
U.S. Pat. No. 3,360,339 teaches a temperature indicating ink which consists of a solution of copper sulfite and a film such as methyl isobutyl ketone. The ink changes color when exposed to moisture above 250.degree. F.
U.S. Pat. No. 3,499,316 teaches a moisture indicating material applied to a mat of inert fibers or paper and discloses the use of cobaltous bromide, magnesium chloride, calcium chloride, aluminum chloride and cobalt chloride as moisture indicators. The indicator of this ink uses a dual salt such as a cobaltous bromide and a bromide salt of zinc, cadmium or mercury as the moisture indicator which changes color.
U.S. Pat. No. 3,548,639 is related to U.S. Pat. No. 3,499,316 and teaches a dual salt moisture indicator of cobaltous bromide and barium chloride or magnesium chloride.
U.S. Pat. No. 3,881,873 teaches a moisture indicator of an aqueous solution of cobaltous chloride.
While the above patents discuss various moisture indicating inks which change color using cobalt chloride as the color changing ingredient or moisture indicator, alcohol as a carrier, and cellulose derivatives as a binder, none of these inks have been found suitable for use as a printing ink on commercial printing or coating equipment at production speeds. Furthermore, none of the heretofore color indicating inks known to us can be applied to a hydrophobic surface such as a glossy or top coated paper.